Semiconductor light-emitting element

ABSTRACT

A semiconductor light-emitting element includes a first semiconductor layer of a first conductive type, a second semiconductor layer of a second conductive type, a light-emitting layer formed between the first semiconductor layer and the second semiconductor layer, a first electrode connected to the first semiconductor layer, and a second electrode connected to the second semiconductor layer. The second electrode includes an ohmic electrode contacting the second semiconductor layer, and a semiconductor electrode made of a semiconductor layer contacting the ohmic electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2014-201775, filed on Sep. 30, 2014, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a semiconductor light-emittingelement.

BACKGROUND

Light-emitting elements, in which nitride semiconductors are used, canemit light from near ultraviolet to red regions by virtue of the widebandgap properties thereof, and accordingly, a variety of research onthese light-emitting elements has been conducted. The general structureof a nitride semiconductor light-emitting element includes asemiconductor laminated structure, in which an n-type nitridesemiconductor layer, an active layer, and a p-type nitride semiconductorlayer are laminated on a substrate. Typically, an electrode is providedon approximately the entire surface of the p-type nitride semiconductorlayer.

In some types of nitride semiconductor light-emitting elements, a lighttransmissive electrode made of a metal oxide, such as indium tin oxide(ITO), is employed as the electrode that is provided on approximatelythe entire surface of the p-type nitride semiconductor layer, and lightis emitted through the light transmissive electrode: The lighttransmissive electrodes made of ITO and the like have high resistivitycompared with metal electrodes, such that the light transmissiveelectrodes must be increased in thickness to obtain sufficient currentdiffusibility. However, an increase in the thickness of the lighttransmissive electrodes may lead to an increase in the light absorbed bythe light transmissive electrodes. In order to solve the aforementionedproblems, Patent Literature 1 (Japanese Unexamined Patent ApplicationPublication No. 2006-156590) discloses that a current diffusion layermade of metallic materials is further provided between the p-typenitride semiconductor layer and the light transmissive electrodes so asto compensate for the current diffusibility of the light transmissiveelectrodes, thereby reducing the thickness of the light transmissiveelectrodes.

However, while the amount is small, absorption of light occurs in alight transmissive electrode made of a metal oxide such, as ITO.Accordingly, a further increase in the light output of the semiconductorlight-emitting element and the suppression of the absorption of light bythe electrodes is desired.

It is an object of certain embodiments of the present invention toprovide a semiconductor light-emitting element that suppresses theabsorption of light by an electrode and realizes a further increase inoptical output.

SUMMARY

A semiconductor light-emitting element according to an embodiment of thepresent invention may include a first semiconductor layer of a firstconductive type, a second semiconductor layer of a second conductivetype, a light-emitting layer formed between the first semiconductorlayer and the second semiconductor layer, a first electrode connected tothe first semiconductor layer, and a second electrode connected to thesecond semiconductor layer. The second electrode further including alight-transmissive connection electrode in contact with the secondsemiconductor layer; and a light-transmissive semiconductor electrodemade of a semiconductor layer, and in contact with the connectionelectrode.

According to the embodiment of the present invention provided above, thesemiconductor light-emitting element that includes the semiconductorelectrode made up of the semiconductor suppresses the absorption oflight by the electrode can be suppressed, and an increase in output canbe realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a semiconductorlight-emitting element according to an embodiment of the presentinvention.

FIG. 2A is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which a semiconductor electrode isgrown on a growth substrate.

FIG. 2B is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which an adhesive layer is formed onthe upper surface of the semiconductor electrode of FIG. 2A, and bondedto a supporting substrate.

FIG. 2C is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which the growth substrate of FIG.2B is removed, and a second ohmic electrode is formed on the surface ofthe semiconductor electrode exposed due to the removal of the growthsubstrate.

FIG. 2D is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which a first conductive-typesemiconductor layer, a light emitting layer, and a secondconductive-type semiconductor layer are grown on the surface of asubstrate.

FIG. 2E is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which a first ohmic electrode isformed on the upper surface of the second conductive-type semiconductorlayer of FIG. 2D.

FIG. 2F is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which the first ohmic electrode ofFIG. 2E and the second ohmic electrode of FIG. 2C are bonded to eachother.

FIG. 2G is a schematic cross-sectional view illustrating a structureproduced by a step in a manufacturing method of the semiconductorlight-emitting element of FIG. 1 in which the adhesive layer and thesupporting substrate of FIG. 2F are removed.

FIG. 3 is a schematic cross-sectional view illustrating a semiconductorlight-emitting element according to a modified embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present embodiment allows the sheet resistance of a semiconductorlayer having high resistivity, compared with metal electrodes, to beequalized with that of the metal electrodes by increasing the thicknessof the semiconductor layer.

Theoretical Considerations

A comparison of current diffusing performance in terms of theresistivity of conventional electrodes made of indium tin oxide (ITO) orAg, and an electrode made of an n-type gallium nitride (n-GaN) ispresented in Table 1 below.

TABLE 1 Material Resistivity (10⁻⁸ Ωm) ITO 150 n-GaN 4700 Ag 1.58

As shown in Table 1, the resistivity of the n-type gallium nitride(n-GaN) is 1,000, or more, times that of the metal, such as Ag, and 10,or more, times that of a conventional light transmissive electrode, suchas ITO. However, the resistivity can be reduced by increasing thethickness, so that an increase in the thickness of an n-GaN layer thatis used as an electrode layer can increase the sheet resistance to thesame degree to that of the metal, such as Ag, or metal oxide, such asITO. For example, an Ag electrode used as a light transmissive electrodeis formed in a thickness of approximately 20 Å to ensure its lighttransmissive property while providing current diffusion. A sheetresistance equivalent to that of the Ag electrode with a thickness ofapproximately 20 Å can be realized with an n-GaN layer with a thicknessof 6 μm, as shown in Table 3 below. It is not difficult to form thenitride semiconductor layer as an element of the semiconductorlight-emitting element having a thickness of several Jim to several tensof μm, so that the semiconductor layer, such as the n-GaN layer, can beutilized as the electrode.

The conventional ITO, the conventional Ag, and the n-type galliumnitride (n-GaN) are compared in terms of optical constants in Table 2.

TABLE 2 Optical Properties Material λ (nm) n k ITO 460 2.000 0.01 n-GaN460 2.450 0.00001 Ag 460 0.151 2.472

In Table 2, n and k represent a real part of a refractive index and animaginary part of the refractive index, respectively, in a complexrefractive index N given by expression (1) below. The complex refractiveindex N is defined by a ratio of a light velocity c in vacuum to a lightvelocity v in a medium.N=n−ik  (1)

Herein, i represents an imaginary number, and i²=−1.

Further, the real part n of the refractive index is generally referredto simply as the refractive index, and the imaginary part k of therefractive index is a value associated with absorption of light, whichis involved with an absorption coefficient α given by expression (2).α=4πk/λ  (2)

Herein, α represents an inverse number of a propagation distance, whichis obtained by reducing the intensity of incident light to the intensityof 1/e, and λ represents the wavelength of light. Further, when thelight advances by a distance d in a film having the absorptioncoefficient α, transmissivity T is given by expression (3).T=exp(−αd)  (3)

The light absorptivity of the n-type gallium nitride (n-GaN) isextremely low, compared with the conventional light transmissiveelectrodes, such as ITO. Thus, an electrode with sufficiently smalllight absorptivity can be realized even in the case where the thicknessof an n-type gallium nitride (n-GaN) layer is increased.

Accordingly, in a case where each thickness is set in such a manner asto obtain the same sheet resistance, the sheet resistivity and theabsorption of light are calculated as shown in Table 3.

TABLE 3 Absorption Sheet Resistance Film Thickness (Vertical Incidence)Material (Ω/Square) (Å) (%) ITO 7.8 1930 5.13 n-GaN 7.8 60000 0.16 Ag7.8 20.2 12.74

As shown in Table 3, the use of an n-type gallium nitride semiconductorlayer made of n-GaN, with a thickness of about 6 μm (60,000 Å) in placeof an ITO electrode with a thickness of about 0.2 μm (1,930 Å) as theelectrode produces a light transmissive electrode which has a sheetresistance approximately equal to the sheet resistance of the ITOelectrode and an extremely low light absorptivity.

As is described above, the thickness of the semiconductor layer made ofthe n-type gallium nitride (n-GaN) is set in such a manner as to obtaina desired resistance value, which allows the semiconductor layer to beutilized as the semiconductor electrode. Furthermore, instead of usingonly the conventional light transmissive electrode such as ITO,utilizing the semiconductor electrode can produce a light transmissiveelectrode having a resistance equivalent to that of conventionalelectrodes while having an extremely small absorption of light comparedwith that of the conventional electrodes. Certain embodiments of thepresent invention has been made in view of the aforementionedtheoretical considerations. Hereinafter, the semiconductorlight-emitting element of embodiments according to the present inventionwill be described.

Semiconducting Light-Emitting Element

A semiconductor light-emitting element of an embodiment according to thepresent invention is a semiconductor light-emitting element thatincludes a semiconductor electrode made of an n-type nitridesemiconductor, and that emits light via the semiconductor electrode.

As illustrated in FIG. 1, light emitting elements according to anembodiment of the present invention include a substrate 1, a firstconductive-type semiconductor layer 3 on the substrate 1, a lightemitting layer 5 disposed on the first conductive-type semiconductorlayer 3, a second conductive-type semiconductor layer 7 disposed on thelight emitting layer 5, a first electrode (i.e. first pad electrode) 41connected to the first conductive-type semiconductor layer 3, and asecond electrode 43 connected to the second conductive-typesemiconductor layer 7. The substrate 1 may include sapphire. The firstconductive-type semiconductor layer 3 may include an n-typesemiconductor. The light emitting layer 5 may include a nitridesemiconductor that contains In. The second conductive-type semiconductorlayer 7 may include a p-type nitride semiconductor. Moreover, the secondelectrode 43 includes a connection electrode 11 provided onapproximately the whole of the upper surface of the secondconductive-type semiconductor layer 7, a semiconductor electrode 23, anda second pad electrode 33 provided on a portion of the upper surface ofthe semiconductor electrode 23. The connection electrode 11 may includeITO, and the semiconductor electrode 23 may include n-type GaN.

The connection electrode 11 may be a bonded body including a first ohmicelectrode 9 and a second ohmic electrode 29.

Examples of specific materials that can be used for each member ofsemiconducting light-emitting element include:

for the first conductive-type semiconductor layer 3: n-GaN;

for the light emitting layer 5: InGaN, InAlGaN;

for the second conductive-type semiconductor layer 7: p-GaN;

for the first ohmic electrode 9: at least one of ITO, Ag, Ti, and Ni,

for the second ohmic electrode 29: at least one of ITO, Ag, Ti, and Al;

for the semiconductor electrode 23: at least one of n-GaN and n-AlGaN;and

for the first pad electrode 41 and the second pad electrode 33:Ti/Al/Ti/Pt/Au (i.e. a stacked body of Ti, Al, Ti, Pt, and Au).

Herein, ITO, Ag, Ti, and Ni, as the first ohmic electrode 9, can beconnected to the p-type nitride semiconductor layer with a low contactresistance, for example, through ohmic contact in the case of formingthe second conductive-type semiconductor layer 7 of a p-type nitridesemiconductor layer, such as p-GaN and the like. Similarly, ITO, Ag, Ti,and Al, as the second ohmic electrode 29, can be connected to the n-typenitride semiconductor layer with low contact resistance, for example,through ohmic contact when the semiconductor electrode 23 formed of then-type nitride semiconductor layer, such as n-GaN, n-AlGaN, or the like.

The thicknesses of the first ohmic electrode 9 and the second ohmicelectrode 29 may differ depending on the materials constituting eachohmic electrode. For example, in the case of forming the first ohmicelectrode 9 or the second ohmic electrode 29 from a metal such as Ag,Ti, or Ni, the thickness can be 0.1 nm to 0.8 nm, preferably 0.1 nm to0.4 nm, and more preferably 0.1 nm to 0.2 nm. Similarly, in the case offorming the first ohmic electrode 9 or the second ohmic electrode 29from a metal oxide such as ITO, the thickness can be 1 nm to 100 nm,preferably from 1 nm to 50 nm, and more preferably from 1 nm to 30 nm.Ohmic contact properties can be maintained with a thickness equal to orgreater than a certain thickness, and the absorption of light by thefirst ohmic electrode 9 can be reduced with a thickness equal to orsmaller than a certain thickness. Although the thicknesses of the firstohmic electrode 9 and the second ohmic electrode 29 can be the same, itis preferable that the thickness of the first ohmic electrode 9 islarger than that of the second ohmic electrode 29. Generally, a numberof protrusions are present on the surface of the p-type nitridesemiconductor layer, which makes it difficult to obtain a flat surfaceon the first ohmic electrode 9. However, by increasing the thickness ofthe first ohmic electrode 9, a flat surface can be obtained on the firstohmic electrode 9.

In the semiconductor light-emitting element configured as describedabove, the connection electrode 11 is made of a metal oxide, such asITO, or a metal, such as Ag, and bonded to the second conductive-typesemiconductor layer 7 and the semiconductor electrode 23 to secure goodelectrical conduction between the second conductive-type semiconductorlayer 7 and the semiconductor electrode 23. That is, if the secondconductive-type semiconductor layer 7 and the semiconductor electrode 23are directly bonded, good electrical conduction may be difficult toestablish due to formation of PN junctions and the like. Accordingly, inthe present embodiment, good electrical conduction between the secondconductive-type semiconductor layer 7 and the semiconductor electrode 23is secured by providing the connection electrode 11 that makes an ohmiccontact to both the second conductive-type semiconductor layer 7 and thesemiconductor electrode 23. Furthermore, in the semiconductorlight-emitting light is emitted via the semiconductor electrode 23 withthe use of the light transmissive property of the semiconductorelectrode 23, such that the connection electrode 11 is provided by, forexample, a light transmissive electrode member, such as ITO.

The connection electrode 11 is configured to bond to the secondconductive-type semiconductor layer 7 and the semiconductor electrode23, while also securing good electrical conduction between the secondconductive-type semiconductor layer 7 and the semiconductor electrode23. The semiconductor electrode 23 serves to diffuse the current appliedvia the second pad electrode 33. Accordingly, the connection electrode11 can be formed with a small thickness compared with conventionalelectrodes used for diffusing the current. For example, in thesemiconductor light-emitting element of the present embodiment, in whichthe light is emitted via the semiconductor electrode 23, the connectionelectrode 11 can be formed with a small thickness compared withconventional light transmissive electrodes, such as ITO, used forcurrent diffusion, and the absorption of light by the connectionelectrode 11 can be reduced significantly as a result. Further, in thesemiconductor light-emitting element of the present embodiment, asdescribed above, even when the thickness of the semiconductor electrode23 used for current diffusion is increased in such a manner as to obtainthe sheet resistance that produces effective diffusion of the current,the absorption of light can be sufficiently reduced. Accordingly, in thesemiconductor light-emitting element of the present embodiment, thesemiconductor electrode 23 has a light transmissive property and is usedfor current diffusion. Thus, an electrode structure with a lowresistivity and substantially no light-absorption can be produced. Thus,a semiconductor light-emitting element that has a high light-extractionefficiency, a high light-emitting efficiency, and a low driving voltagecan be provided.

The semiconductor electrode 23 can have a thickness of 2 μm to 200 μm,preferably 3 μm to 20 μm, and more preferably 4 μm to 10 μm. Asdescribed above, when the semiconductor electrode 23 is above a certainthickness, the resistivity can be reduced, such that the current can beefficiently applied. Also, when the semiconductor electrode 23 is belowa certain thickness, influence of a warpage caused by the difference inthermal expansion between the semiconductor electrode and a growthsubstrate during the manufacture of the semiconductor electrode can bereduced, such that an improvement in a process yield rate can beexpected.

Subsequently, a method of manufacturing a semiconductor light-emittingelement of the present embodiment will be described. The method ofmanufacturing a semiconductor light-emitting element of the presentembodiment includes forming a semiconductor electrode, forming asemiconductor stacked-layer structure, and forming an electrodestructure. The step of forming a semiconductor electrode and the step offorming a semiconductor stacked-layer structure can be performed inparallel, and the step of forming an electrode structure is performedafter the step of forming a semiconductor electrode and the step offorming a semiconductor stacked-layer structure.

Forming Semiconductor Electrode

In the present method of manufacturing, as illustrated in FIG. 2A,first, the semiconductor electrode 23 made of the nitride semiconductor,such as n-type GaN, is grown on a growth substrate 21, such as sapphire.The semiconductor electrode may be grown via a buffer layer. In thesemiconductor light-emitting element according to the present embodimentthat is configured to emit light through the semiconductor electrode 23,a semiconductor material which has a bandgap greater than that of thesemiconductor material which constitutes the light emitting layer isselected for a semiconductor material to constitute the semiconductorelectrode 23. In the case of employing a multiple quantum well structuremade of well layers and barrier layers for the light emitting layer, asemiconductor material which has a bandgap greater than that of the welllayers is selected. Further, a semiconductor material that can obtain alow resistivity by addition of dopant may be selected. For example, in anitride semiconductor light-emitting element, in the case where anitride semiconductor that contains indium is used as the light emittinglayer, a n-type GaN or a n-type AlGaN doped with silicon or germaniumcan be selected as the semiconductor material for the semiconductorelectrode 23. In the case of the n-type GaN, it is preferable that theconcentration of the dopant be increased to an extent that does notimpair crystallinity, and thus the concentration of the dopant can be,for example, 1×10¹⁸/cm³ to 1×10¹⁹/cm³. In the case of the n-type AlGaN,the concentration of the dopant can be, for example, 1×10¹⁸/cm³ to1×10¹⁹/cm³. Further, a n-type GaN can be grown to a large thickness withgood crystallinity, such that it can be used as a preferable materialfor a nitride semiconductor light-emitting element that emits a visiblelight, such as a blue light. Also, n-type AlGaN has a bandgap largerthan that of GaN, and absorption of ultraviolet rays can be reduced withan increase in the ratio of Al, such that the n-type AlGaN can be usedas a preferable material for a nitride semiconductor light-emittingelement that emits ultraviolet rays. The mixed crystal ratio of Al inthe n-type AlGaN can be, in the case of assuming AlxGa1−xN (1>x>0), canbe 0.02≦x≦0.1, preferably, 0.02≦x≦0.06.

Subsequently, as illustrated in FIG. 2B, on the upper surface of thesemiconductor electrode 23, an adhesive layer 25 is formed, and asupporting substrate 27 is bonded to the adhesive layer 25. The adhesivelayer 25 may be formed of an adhesive resin, such as a thermosettingresin. The supporting substrate 27 may include sapphire. Subsequently,as illustrated in FIG. 2C, the growth substrate 21 is removed by using alaser lift-off method, or the like. More specifically, a laser beam of awavelength which allows the laser beam to penetrate the growth substrate21 and is absorbed by the semiconductor material constituting thesemiconductor electrode 23 is selected. The laser beam is emitted fromthe growth substrate 21 side to rise a temperature in the vicinity ofthe interface between the growth substrate 21 and the semiconductorelectrode 23 to ablate (degrade) the adhesive layer 25, thereby removingthe growth substrate 21.

After the removal of the growth substrate 21, the surface of thesemiconductor electrode 23 is polished by a chemical mechanicalpolishing method, or the like, to obtain a smooth surface of thesemiconductor electrode 23. Then, as illustrated in FIG. 2C, a secondohmic electrode 29 is formed on the surface of the semiconductorelectrode 23 that is exposed by removing the growth substrate 21. Thesecond ohmic electrode 29 may be made of, for example, a metal oxide,such as ITO, or a metal, such as Ag.

Forming Semiconductor Stacked-layer Structure

In the step of forming a semiconductor stacked layer structure, first, asubstrate 1 is provided. The substrate 1 may include sapphire.Subsequently, as illustrated in FIG. 2D, a surface of the substrate 1for growing a semiconductor layer is processed to formrecesses/protrusions. The processing of the surface of the substrate 1to form recesses/protrusions is optional. The surface processing can beperformed by setting the conditions on the shape and the dimensions of amask and the conditions of etching, according to the crystal form of thesubstrate and the plane orientation of the surface of the substrate onwhich the recesses/protrusions are to be formed, so as to obtain atarget surface geometry.

For example, in the case of forming a circular mask on a surface of aC-plane of a sapphire substrate and etching the substrate, in an earlystage of etching, portions which are not provided with the mask areremoved by the etching, and circular protrusions approximatelycorresponding to the shape of the mask are formed. Then, as the etchingprogresses, due to the influence of directional dependency in theetching rate attributed to crystal forms (the progress of etchingdiffers depending on the direction of crystal orientation) the circularprotrusions are formed into shapes reflected on the crystal forms. Theformation of the protrusions allows the growth of the semiconductorlayer with good crystallinity and good light-extraction efficiency.

Subsequently, as illustrated in FIG. 2D, a first conductive-typesemiconductor layer 3, a light emitting layer 5, and a secondconductive-type semiconductor layer 7 are grown on the treated surfaceof the substrate 1, thereby manufacturing the semiconductorstacked-layer structure. The semiconductor layer 3 may include an n-typesemiconductor. The light emitting layer 5 may include a nitridesemiconductor which contains indium. The second conductive-typesemiconductor layer 7 may include a p-type nitride semiconductor.Furthermore, as illustrated in FIG. 2E, a first ohmic electrode 9 isformed on the entire upper surface of the second conductive-typesemiconductor layer 7. The first ohmic electrode 9 may include ITO.

After the formation of the first ohmic electrode 9, the surface of thefirst ohmic electrode 9 may be planarized by a known method, such asChemical Mechanical Polishing (CMP). At the time of growing thesemiconductor layer, irregularities may be formed on the surface of thep-type nitride semiconductor layer. Subsequently, irregularities may begenerated on the surface of the first ohmic electrode 9, that may leadto difficulty in bonding with the second ohmic electrode 29. In suchcases, planarizing the surface of the first ohmic electrode 9 canfacilitate the bonding between the first ohmic electrode 9 and thesecond ohmic electrode 29.

Forming Electrode Structure

The first ohmic electrode 9 (as shown in FIG. 2E) formed on the entireupper surface of the second conductive-type semiconductor layer 7 havingthe semiconductor stacked-layer structure and the second ohmic electrode29 (as shown in FIG. 2C) formed on the surface of the semiconductorelectrode 23 supported by the supporting substrate 27 are bonded byusing a room-temperature bonding method (as shown in FIG. 2F). In thepresent embodiment, a surface activation bonding method is used as theroom-temperature bonding method. The surface activation bonding methodis a method in which after a bonding interface is activated by applyingion beams or plasmas to the bonding surfaces, the members are directlybonded by contacting the activated surfaces thereof. According to thesurface activation bonding method, materials can be bonded directly toeach other without any intervening elements. In the present embodiment,the connection electrode 11, which is the bonding body of the firstohmic electrode 9 and the second ohmic electrode 29, is made of ITO.

In the present embodiment, the surface activation bonding method is usedas the room-temperature bonding method, but an atomic diffusion bondingmethod can also be applied as a bonding method. Further, thermalcompression or the like can also be used as the bonding method.

The atomic diffusion bonding method is a method in which superimposingthin layers of metal layers in vacuum generates atomic diffusion at thebonding interface and crystal grain boundary, which bonds the layersfirmly to each other. Moreover, the atomic diffusion bonding methodenables not only bonding between similar materials, for example bondingbetween metals, but also bonding between different materials, forexample bonding between a metal and a semiconductor, between a metaloxide and a semiconductor, or bonding between a metal and a metal oxide.Furthermore, in the case of employing an atomic diffusion bonding methodfor the bonding, the thicknesses of the first ohmic electrode 9 and thesecond ohmic electrode 29 may be, for example, 20 nm or less. Asdescribed above, the thickness of the connection electrode 11 can beextremely small, so that the absorption of light by the connectionelectrode 11 can be reduced. In the case of bonding by an atomicdiffusion bonding method, an atomic diffusion layer may be formedbetween the first ohmic electrode 9 and the second ohmic electrode 29. Abond of high uniformity can be easily realized by providing the atomicdiffusion layer. The atomic diffusion layer between the first ohmicelectrode 9 and the second ohmic electrode 29 is made of a metal, forexample, Au, Ti, or the like. In this case, the atomic diffusion layeris formed with a small thickness to an extent such that light is notsubstantially absorbed by the atomic diffusion layer. The thickness ofthe atomic diffusion layer may depend on the material of the atomicdiffusion layer. In the case of Au, the atomic diffusion layer may beformed with a thickness of, for example, 0.1 μm to 0.4 μm.

In the present embodiment, the semiconductor electrode 23 grown on thegrowth substrate 21 is bonded to the supporting substrate 27 before thestep of forming the electrode structure. Due to the difference inthermal expansion between the semiconductor electrode and the growthsubstrate, during manufacturing, a semiconductor electrode may beprojectingly warped to the semiconductor electrode side. However, such awarpage can be reduced by bonding the semiconductor electrode 23 to thesupporting substrate 27, thus facilitating the bonding of the secondohmic electrode 29 provided on the semiconductor electrode to the firstohmic electrode 9 formed on the entire upper surface of the secondconductive-type semiconductor layer 7 that has the semiconductorstacked-layer structure. The step of bonding the semiconductor electrode23 to the supporting substrate 27 is optional, and the semiconductorelectrode 23 grown on the growth substrate 21 can be provided directlyto the next forming step. In this case, after the formation of thesemiconductor electrode 23, the surface of the semiconductor electrode23 is polished. In this manner, the step of bonding the semiconductorelectrode 23 to the supporting substrate 27 is omitted, such thatproductivity can be improved.

Subsequently, as illustrated in FIG. 2G, the adhesive layer 25 and thesupporting substrate 27 are removed. More specifically, a laser beam ofa wavelength which penetrates the supporting substrate 27 and isabsorbed by the semiconductor material that constitutes thesemiconductor electrode 23 is selected. Then, the laser beam is emittedfrom the supporting substrate 27 side to raise the temperature in thevicinity of the interface between the supporting substrate 27 and theadhesive layer 25 to ablate (degrade) the adhesive layer 25, therebyremoving the supporting substrate 27. Subsequently, the adhesive layer25 is removed by ashing with oxygen or by using a chemical solution suchas sulfuric acid. In particular, with the use of a chemical solutionsuch as sulfuric acid, damage on the semiconductor electrode 23 can besatisfactorily reduced.

After the adhesive layer 25 and the supporting substrate 27 are removed,portions of the semiconductor electrode 23, the second conductive-typesemiconductor layer 7, and the light emitting layer 5 disposed on anelectrode forming surface are removed in order to expose a portion ofthe first conductive-type semiconductor layer 3 (i.e. the electrodeforming surface). Subsequently, a first electrode 41 is formed on theelectrode forming surface of the first conductive-type semiconductorlayer 3, and a second pad electrode 33 is formed on a portion of thesurface of the semiconductor electrode 23. For example, the firstelectrode 41 and the second pad electrode 33 can be formed ofstacked-layer bodies of the same configuration that includes Ti, Al, Ti,Pt, and Au, and may be formed in the same step.

As described above, the semiconductor light-emitting element illustratedin FIG. 1 according to the first embodiment is manufactured.

The aforementioned semiconductor light-emitting element of the presentembodiment is configured to emit light through the semiconductorelectrode 23. The semiconductor light-emitting element may be configuredsuch that a light reflection layer made of a dielectric multilayer filmis provided on the semiconductor electrode, and light is emitted from alight transmissive substrate 1, such as sapphire. Even in a case wherethe light is emitted from the substrate 1 side, absorption of the lightby the electrode occurs at the time of extracting the light byreflecting the light that is propagating toward the electrode side, andaccording to the present embodiment, the absorption by the electrode canbe reduced, such that the light emitting efficiency can be improved.

In the semiconductor light-emitting element of the present embodiment,the first ohmic electrode 9 formed on the second conductive-type nitridesemiconductor layer and the second ohmic electrode 29 formed on thesemiconductor electrode 23 are bonded. However, as shown in FIG. 3, thesemiconductor light-emitting element may be configured such that theconnection electrode is formed on either the second conductive-typenitride semiconductor layer or the semiconductor electrode 23, and theconnection electrode is directly connected to the other of the secondconductive-type nitride semiconductor layer or the semiconductorelectrode 23. Alternatively, after forming the connection electrode onthe second conductive-type nitride semiconductor layer, thesemiconductor electrode 23 may be directly formed on the connectionelectrode, such as by using a spattering method (e.g., an ElectronCyclotron Resonance (ECR) spattering method).

It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

What is claimed:
 1. A method of manufacturing a semiconductor lightemitting element, the method comprising: providing a first stacked-bodythat includes, in the following order: a substrate, a firstsemiconductor layer of a first conductive type, a light-emitting layer,a second semiconductor layer of a second conductive type, and a firstohmic electrode; providing a second stacked-body that includes, in thefollowing order: a supporting substrate, a semiconductor electrode, anda second ohmic electrode; bonding the first ohmic electrode and thesecond ohmic electrode; removing the supporting substrate; removingportions of the semiconductor electrode, the second ohmic electrode, thefirst ohmic electrode, the second semiconductor layer, the lightemitting layer, and the first semiconductor layer, in that order, toexpose an electrode forming surface of the first semiconductor layer;and forming a first pad electrode on the electrode forming surface ofthe first semiconductor layer, and a second pad electrode on a portionof a surface of the semiconductor electrode.
 2. The method ofmanufacturing a semiconductor light emitting element according to claim1, wherein providing the second stacked-body comprises: growing thesemiconductor electrode on a growth substrate, bonding the supportingsubstrate on the semiconductor electrode, removing the growth substrate,polishing a lower surface of the semiconductor electrode, and formingthe second ohmic electrode on the lower surface of the semiconductorelectrode.
 3. The method of manufacturing a semiconductor light emittingelement according to claim 2, wherein bonding the first ohmic electrodeand the second ohmic electrode comprises a surface activation bondingmethod or an atomic diffusion bonding method.
 4. The method ofmanufacturing a semiconductor light emitting element according to claim3, further comprising planarizing a surface of the first ohmic electrodebefore bonding the first ohmic electrode and the second ohmic electrode.5. A method of manufacturing a semiconductor light emitting element, themethod comprising: providing a first stacked-body which includes, in thefollowing order: a substrate, a first semiconductor layer of a firstconductive type, a light-emitting layer, a second semiconductor layer ofa second conductive type, and a first ohmic electrode; forming a secondstacked-body by performing steps comprising: growing a semiconductorelectrode on a growth substrate, and forming a second ohmic electrode ona surface of the semiconductor electrode; and bonding the first ohmicelectrode and the second ohmic electrode; removing the growth substrate;removing portions of the semiconductor electrode, the second ohmicelectrode, the first ohmic electrode, the second semiconductor layer,the light emitting layer, and the first semiconductor layer, in thatorder, to expose an electrode forming surface of the first semiconductorlayer; and forming a first pad electrode on the electrode formingsurface of the first semiconductor layer, and a second pad electrode ona portion of a surface of the semiconductor electrode.
 6. The method ofmanufacturing a semiconductor light emitting element according to claim5, wherein forming the second stacked-body further comprises: polishingthe surface of the semiconductor electrode before forming the secondohmic electrode.
 7. The method of manufacturing a semiconductor lightemitting element according to claim 6, wherein bonding the first ohmicelectrode and the second ohmic electrode comprises a surface activationbonding method or an atomic diffusion bonding method.
 8. The method ofmanufacturing a semiconductor light emitting element according to claim7 further comprising planarizing a surface of the first ohmic electrodebefore bonding the first ohmic electrode and the second ohmic electrode.9. A method of manufacturing a semiconductor light emitting element, themethod comprising: providing a first stacked-body that includes, in thefollowing order: a substrate, a first semiconductor layer of a firstconductive type, a light-emitting layer, a second semiconductor layer ofa second conductive type, and a first ohmic electrode; providing asecond stacked-body that includes, in the following order: a supportingsubstrate, a semiconductor electrode, and a second ohmic electrode;bonding the first ohmic electrode and the second ohmic electrode; andremoving the supporting substrate, wherein providing the secondstacked-body comprises: growing the semiconductor electrode on a growthsubstrate, bonding the supporting substrate on the semiconductorelectrode, removing the growth substrate, polishing a lower surface ofthe semiconductor electrode, and forming the second ohmic electrode onthe lower surface of the semiconductor electrode.
 10. The method ofmanufacturing a semiconductor light emitting element according to claim9, wherein bonding the first ohmic electrode and the second ohmicelectrode comprises a surface activation bonding method or an atomicdiffusion bonding method.
 11. The method of manufacturing asemiconductor light emitting element according to claim 10, furthercomprising planarizing a surface of the first ohmic electrode beforebonding the first ohmic electrode and the second ohmic electrode.